The present invention is directed to bicycles and, more particularly, to a method and apparatus for controlling the operation of a bicycle transmission to compensate for power supply characteristics.
Bicycle transmissions that are operated by an electric motor or the like have recently become known. Such transmissions may be shifted automatically according to the bicycle speed or shifted manually by the rider. Typically, a shift command is generated according to the bicycle speed or manual input by the rider, the motor is controlled by a transmission operating unit in response to the shift command, and the gear ratio of the transmission is set accordingly.
For example, U.S. Pat. No. 6,162,140 discloses a motor driven derailleur that includes a base member, a movable member, and a linkage mechanism. The linkage mechanism includes a link member coupled to the base member and to the movable member so that the movable member moves relative to the base member. The link member is pivotally coupled to one of the base member and the movable member through a link coupling member, and a motor is provided for rotating the link-coupling member. The movable member moves relative to the base member in response to rotation of the link-coupling member.
U.S. Pat. No. 5,357,177 discloses an electrical adjustment device for an electrical chain transfer device for bicycles. The adjustment device comprises an adjusting element, a drive device for moving the adjusting element, and a control unit for controlling the drive device. A presetting device is operatively coupled to the control unit for storing a plurality of set values, wherein each set value corresponds to an operational position of the adjusting element and therefore the chain transfer device. The adjusting element can be moved to a desired set position, and then the set position value can be stored in the presetting device to replace a former set position value and thereby establish or fine tune an operating position of the chain transfer device.
U.S. Pat. No. 6,740,003 discloses an apparatus for moving an electrically controlled bicycle derailleur from a first sprocket to a second sprocket. The apparatus comprises a derailleur position input for receiving a signal from a potentiometer mounted to the derailleur that indicates a position of the derailleur, a memory for storing a reference derailleur position for the second sprocket, and a motion control circuit that provides a plurality of signals to move the derailleur from the first sprocket to the second sprocket. The plurality of signals comprises a first signal generated when the derailleur initially moves away from the first sprocket and a second signal generated when the derailleur is in close proximity to the second sprocket. The second signal prevents the derailleur from overshooting the second sprocket.
In such known systems, the speed of the motor that operates the various positioning elements depends on various characteristics of the power supply, such as voltage. For example, if the power supply voltage is higher than the designed operating voltage for the motor, possibly caused by high ambient temperature or high charging voltage from a wheel generator, then the motor shaft used to operate a derailleur may rotate faster than expected. If the sampling rate for the position sensor is not sufficiently high, then the derailleur may overshoot the destination sprocket and may even cause the chain to engage the sprocket beyond the destination sprocket. Thus, properly controlling the motor can become very difficult, including attempts to move the derailleur back to the proper position.